Active pharmaceutical ingredients (APIs) can be prepared in a variety of different forms, for example, chemical derivatives, solvates, hydrates, co-crystals, or salts. APIs may also be prepared in different solid forms, in that they may be amorphous, may exist as different crystalline polymorphs, and/or in different solvation or hydration states. By varying the form of an API, it is possible to vary the physical properties thereof. For instance, solid forms of an API typically have different solubilities such that a more thermodynamically stable solid form is less soluble than a less thermodynamically stable solid form. Solid forms can also differ in properties such as shelf-life, bioavailability, morphology, vapor pressure, density, color, and compressibility. Accordingly, variation of the solid state of an API is one of many ways in which to modulate the physical and pharmacological properties thereof.
Bendamustine, 4-{5-[Bis(2-chloroethyl)amino]-1-methyl-2-benzimidazolyl}butyric acid:

Bendamustine Hydrochloride was initially synthesized in 1963 in the German Democratic Republic (GDR) and was available from 1971 to 1992 there under the tradename Cytostasan®. See, e.g., W. Ozegowski and D. Krebs, IMET 3393 γ-[1-methyl-5-bis-(β-chloroethyl)-aminobenzimidazolo-(2)]-butyryl chloride, a new cytostatic agent of the group of benzimidazole nitrogen mustards. Zbl. Pharm. 110, (1971) Heft 10, 1013-1019, describing the synthesis of bendamustine hydrochloride monohydrate. Since that time, it has been marketed in Germany under the tradename Ribomustin®. Bendamustine is an alkylating agent that has been shown to have therapeutic utility in treating diseases such as chronic lymphocytic leukemia, Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma, and breast cancer.
While bendamustine has been demonstrated as efficacious, it is known to be unstable, especially in aqueous solutions, leading to technical difficulties in its preparation and administration. Researchers, therefore, have investigated methods of improving the preparation and stability of bendamustine and its formulations. For example, German (GDR) Patent No. 159877 discloses a method for preparing bendamustine free base by reaction of the bis-hydroxyl precursor with thionyl chloride followed by recrystallization from water.
German (GDR) Patent No. 34727 discloses a method of preparing derivatives of bendamustine. The described derivatives differ from bendamustine in the substitution at the 1-position.
German (GDR) Patent No. 80967 discloses an injectable preparation of bendamustine hydrochloride monohydrate, ascorbic acid, and water. GDR 80967 describes that lyophilization of compounds such as bendamustine is only possible if the compound is of sufficient stability that it can withstand the processing conditions. The preparation described in GDR 80967 is not lyophilized.
German (GDR) Patent No. 159289 discloses a ready-to use, injectable solution of bendamustine hydrochloride that avoids lyophilization. GDR 159289 describes an anhydrous solution of bendamustine hydrochloride in 1,2-propylene glycol or ethanol.
U.S. application Ser. No. 11/330,868, filed Jan. 12, 2006, assigned to Cephalon, Inc., Frazer, Pa., discloses methods of preparing lyophilized pharmaceutical compositions comprising bendamustine hydrochloride.
In light of the potential benefits of different solid forms of APIs and in light of the efficacy of bendamustine, a need exists to identify and prepare novel solid forms of bendamustine hydrochloride.